Recycling of electric arc furnace slag from hydrogen-based iron production in cementitious binders

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Synthetic glass with high alkali-reactivity and near-zero RM- CO2 emissions

As cement-related CO2 emissions increase, alternatives are actively sought. Cement substitution by slag and fly ash is standard practice worldwide and while higher side stream utilization is necessary, their volumes are not adequate to significantly alter global CO2 emissions. Cement substitution by, and alkali activation of, calcined clays offer an alternative with zero raw-material-related CO2 (RM-CO2) emissions. Please click Additional Files below to see the full abstract

Alkali-activated mineral wools

Mineral wools –a general term for stone wool and glass wool– are the most common building insulation materials in the world. The amount of mineral wool waste generated in Europe totaled 2.3 Mt in 2010 – including wastes from mineral wool production and from construction and demolition industry. Unfortunately, mineral wools are often unrecyclable due to their fibrous nature (Figure 1) and low density. Thus, the utilization of mineral wool waste in post-consumer products remains low. Please click Additional Files below to see the full abstract

Geopolymer matrix for the inertization of gold mine tailings

The mining industry produces a huge amount of solid waste materials during mining’s lifetime. Solid mine tailings typically contain many sulfide minerals and heavy metals. These fine-grained residues are usually deposited in impounding lakes near mining sites. Sulfides are oxidized in contact with water, which decreases the surrounding pH, and metal oxides are leached into the environment. This leachability causes short- and long-term environmental problems, such as contamination of surface and ground water. There is increasing interest in discovering new methods to manage mine tailings more effectively in the future. This interest is mainly focused on developing low-cost treatment or confinement processes. The possibility of immobilizing several heavy metals from gold mine tailings by reactive geopolymerization technique has been investigated in the present study. The chemical stability of geopolymers synthesized by the alkali activation of metakaolin and blast furnace slag with the addition of 40 to 50 wt% gold mine tailings is demonstrated. The geopolymers were cured at room temperature, and the effects of different Si/Al and Na/Al molar ratios and curing times were investigated. The inertization effectiveness was evaluated by means of leaching tests carried out according to standard EN 12457 after 7 and 28 days and after 18 months. The samples were immersed into the water for 1 day, and the leachable metals in the test solution were determined by ICP-OES. Please click Additional Files below to see the full abstract

Geopolymers from mining tailings for more sustainable raw material supply

For ecologic and economic reasons tailings, waste rock and water management become progressively important factors in the mining industry. The European Union funded project ‘Integrated mineral technologies for more sustainable raw material supply’ (ITERAMS) aims to (1) close the water cycle of the mineral processing plant (i.e. minimizing the release of wastewater to the adjacent environment), and (2) to use tailings (and waste rock) as raw materials for geopolymers. This will (1) enable significantly more efficient water recycling at the mining sites, (2) deliver cost savings and added income due to the valorisation of solid waste residues, and (3) minimize the overall environmental footprint of the mining industry and will therefore help improving its performance and as a consequence its social position. The developed solutions influence the total lifecycle of the mining operation, as they provide input to project planning and operational phases as well as to the closure and recultivation. In this paper, the valorisation of the tailings and the waste rock is discussed. The main applications of the geopolymer products are (1) backfill material to fill open cavities from the mining operation and (2) a cover for surface deposits of tailings to store them environmentally safe – i.e. seal them off from surface water streams and oxidising conditions

Utilization of sulphidic mine tailings in alkali-activated materials

Disposal of mine tailings is one of the most important environmental issues during the mining lifetime. Especially sulphidic tailings can cause environmental and ecological risks because of their tendency to oxidize in the presence of water or air. Because of small particle size and harmful chemical properties, utilization possibilities of sulphidic mine tailings are limited. The aim of the present study was to develop technologies to utilize sulphidic mine tailings in alkali activated materials. Alkali-activated materials also known as geopolymers are nanosized zeolite type or slightly amorphous materials comparable to traditional Portland cement concrete, which can physically encapsulate or chemically stabilize the hazardous elements such as heavy metals into the 3D structure. Mine tailing based geopolymer aggregates were successfully produced from sulphidic mine tailings with good physical properties. The geopolymer aggregates performed as a concrete aggregate comparable to commercial lightweight aggregates. In addition, geopolymer mortars were prepared from mine tailings. In mortar application, there is a need to add some co-binder such as blast furnace slag in order to achieve high strength for the material. The mine tailing based geopolymer structure has an ability to stabilize a large number of cationic species into the structure while some anionic species were not able to immobilize by alkaline activation

Characterization of an aged alkali-activated slag roof tile after 30 years of exposure to Northern Scandinavian weather

Alkali-activated materials (AAMs) have been known as an alternative cementitious binder in construction for more than 120 years. Several buildings utilizing AAMs were realized in Europe in the 1950s–1980s. During the last 30 years, the interest towards AAMs has been reinvigorated due to the potentially lower CO2 footprint in comparison to Portland cement. However, one often-raised issue with AAMs is the lack of long-term studies concerning durability in realistic conditions. In the present study, we examined a roof tile, which was prepared from alkali-activated blast furnace slag mortar and exposed to harsh Northern Scandinavian weather conditions in Turku, Finland, for approximately 30 years. Characterization of this roof tile provides unique and crucial information about the changes occurring during AAM lifetime. The results obtained with a suite of analytical techniques indicate that the roof tile had maintained excellent durability properties with little sign of structural disintegration in real-life living lab conditions, and thus provide in part assurance that AAM-based binders can be safely adopted in harsh climates. The phase assemblage and nanostructural characterization results reported here further elucidate the long-term changes occurring in AAMs and provide reference points for accelerated durability tests and thermodynamic modelling

Mechanisms of thermomechanical pulp refining

Abstract The objective of this thesis was to obtain new information about mechanisms of thermomechanical pulp refining in the inner area of a refiner disc gap by studying inter-fibre refining and by calculating the distribution of energy consumption in the refiner disc gap. The energy consumption of thermomechanical pulping process is very high although theoretically a small amount of energy is needed to create new fibre surfaces. Mechanisms of refining have been widely studied in order to understand the high energy consumption of the process, however, phenomena in the inner area of disc gap has had less attention. It is likely that this important position is causing high energy consumption due to the high residence time of pulp located there. The power distribution as a function of the refiner disc gap was calculated in this work. The calculation was based on mass and energy balances, as well as temperature and consistency profiles determined by mill trials. The power distribution was found to be dependent on segment geometry and the refining stage. However, in the first stage refiner with standard refiner segments, a notable amount of power was consumed in the inner area of the disc gap. Fibre-to-fibre refining is likely to be the most important mechanism in the inner area of disc gap from the point of view of energy consumption. In this work the inter-fibre refining was studied using equipment for shear and compression. Fibre-to-fibre refining was found to be an effective way to refine fibres from coarse pulp to separated, fibrillated and peeled fibres if frictional forces inside the compressed pulp were high enough. It was proposed that high energy of today’s thermomechanical pulping process could derive from too low frictional forces that heated pulp and evaporated water without any changes in fibre structure. The method to calculate power distribution and results of fibre-to-fibre refining experiments may give ideas for developing today’s thermomechanical pulp refiners’ or for developing totally new energy saving mechanical pulping processes